It is known to use electromagnetic inductors of the transmitting-field type for this purpose. Such inductors are described particularly in FR No. 2,583,249. In general terms, they comprise a C-shaped magnetic yoke, the ends of the C which form the two poles of the inductor carrying the induction coils being located on either side of the product to be heated.
To maintain high efficiency, the poles must be as near as possible to the product. This means that the poles and the induction coils which they carry are subjected to a high degree of thermal radiation from the hot product. Moreover, under industrial operating conditions, for example during the heating of the edges of slabs or rolled products, the inductors and especially their poles are subjected to chemical and mechanical attacks, for example considerable splashing, the deposition of scale and the risk of impact with the heated product.
A known device for protecting the poles consists of a plate made of porous refractory and is placed on the face of the pole confronting the product, this refractory being cooled by internal air circulation. These devices afford good thermal protection, but nevertheless have the disadvantage of easily oxidizing and becoming clogged and of being attacked by the scale coming from the heated product. This results in the need to replace this porous refractory somewhat frequently, thus making it necessary to shut down the installation, thereby incurring operating costs which are added to the high cost of the said refractory.